1. Field of the Invention
This invention relates to thickener compositions, which are distinguished by exceptionally low viscosity (i.e. the viscosity of the concentrated aqueous solutions of the compositions) combined with a high thickening action, and to their use for thickening aqueous systems.
2. Description of the Prior Art
Polyurethane thickeners for aqueous systems are described in numerous publications (see e.g. DE-OS 1,444,243, DE-OS 3,630,319, EP-A-0,031,777, EP-A-0,307,775, EP-A-0,495,373, U.S. Pat. No. 4,079,028, U.S. Pat. No. 4,155,892, U.S. Pat. No. 4,499,233 and U.S. Pat. No. 5,023,309).
Common to all of these known thickeners is the simultaneous presence of (i) hydrophilic segments in a quantity of at least 50% by weight, (ii) hydrophobic segments in a quantity of at most 10% by weight and (iii) urethane groups. The "hydrophilic segments" in these thickeners are primarily polyether chains having at least 5 alkylene oxide units as chain segments in which at least 60 mol-% of these units are ethylene oxide units. The "hydrophobic segments" are primarily hydrocarbon segments having at least 6 carbon atoms.
These polyurethane thickeners are suitable as auxiliary agents for adjusting the flow properties of aqueous systems such as automotive and industrial lacquers, paints and substances for coloring plaster, printing and textile colors, pigment printing pastes, pharmaceutical preparations and cosmetic preparations, formulations for plant protective agents, filler dispersions, etc.
Although the known polyurethane thickeners have a wide range of application, they have one major disadvantage: They are very difficult to incorporate into aqueous systems because their viscosity when in the form of an aqueous solution is too high.
Many experiments have been carried out in the past to reduce the viscosity of the thickeners. It was attempted to lower the viscosity during preparation of the thickeners, e.g., by lowering their molecular weight, but this always resulted in a reduction in the thickening effect within a homologous series.
The viscosity of aqueous solutions of polyurethane thickeners could also be reduced by adding emulsifiers such as alkoxylated alcohols or phenols. However, this method has the disadvantage that these emulsifiers must be used at high concentrations in order to produce a sufficient lowering of the, viscosity of the thickener. Even then, the viscosity of the thickeners cannot always be lowered to the required level, especially in the case of highly active thickeners.
Another commonly used method for lowering the internal viscosity of aqueous polyurethane thickener solutions is the addition of water-miscible solvents such as water-miscible monohydric or polyhydric alcohols. The main disadvantage of this otherwise highly effective method is the environmental concerns regarding the use these solvents, especially since the quantity of solvents required for obtaining the desired viscosity is often relatively high. Relatively large proportions of solvents may also impair the stability of the aqueous preparations or their properties in use, e.g., the ease with which they can be brush coated.
The obvious disadvantage of reducing the viscosity of the aqueous solutions by dilution with water is, of course, accompanied by an undesirable reduction in the concentration of the active substance (thickener) and hence a reduction in the thickening effect for a given total quantity of solution.
It is an object of the present invention to provide new polyurethane thickener compositions for aqueous systems which in the form of their aqueous solutions or dispersions have a substantially lower viscosity than analogous known systems, but which provide an at least equally good thickening effect.
It was surprisingly found that this problem could be solved by adding to the polyurethane thickener certain triple unsaturated alcohols of the type described below as component c) in addition to known emulsifiers. It was observed that the simultaneous addition of the components b) and c) described below has a synergistic action in lowering the viscosity. For a given concentration of emulsifiers b) the viscosity of the aqueous solutions or dispersions is substantially reduced in the presence of auxiliaries c) or conversely, much lower concentrations of emulsifiers b) are required for obtaining comparable viscosities in the presence of auxiliaries c).